Each faction type has access to its own tech tree. The kind of technology that can be found within these tech trees are generally specific to the faction type.
As with any tree, technology within a tech tree must be unlocked sequentially. You can not unlock technology that you do not have the preceding tecchnology for.
A player will not know what technology is that they are able to unlock, until they've unlocked it. However, a player can guess at the kind of technology based on the points cost.

Example

A ship with better engines will cost more in engines research.

There are two different types of technologies on the tech tree. Stock technology and variant technology.
Unique technologies involves a higher point cost but will unlock a new type of entity, while a variant technology will, for a smaller point cost,
unlock a variant of an entity you already have.

Variants allow for more product choice with your customers as well as for your own fleets, so while they may not be as interesting as new technology, for a smaller point cost
they can allow you to differentiate your fleet.